Superstring Theory: 5 Needed Breakthroughs -- John H. Schwarz

John H. Schwarz (photo credit: Patricia Schwarz)

[In 2001, Prof. John Preskill of Caltech wrote a poem "To John Schwarz" (full text here) which started as ..

"Thirty years ago or more
John saw what physics had in store.
He had a vision of a string
And focused on that one big thing."

The name 'Schwarz' is intimately associated with the origin and evolution of Superstring theory. In 1971 John Schwarz and André Neveu developed an early version of superstring theory, which led among other things to the discovery of supersymmetry. In 1974 Joël Scherk and he proposed that string theory should be used to construct a unified quantum theory containing gravitation.

In 1984 Michael Green and he discovered an anomaly cancellation mechanism, which resulted in string theory becoming one of the hottest areas in theoretical physics. As Prof. Preskill's poem describes:

If you weren't there you couldn't know
The impact of that mightly blow:
"The Green-Schwarz theory could be true ---
It works for S-O-thirty-two!"

John Schwarz is the Harold Brown Professor of Theoretical Physics at California Institute of Technology (Caltech) where he taught and conducted research since 1972. He received the Dirac Medal of the International Centre for Theoretical Physics, Trieste in 1989, as well as the Dannie Heineman Prize for Mathematical Physics of the American Physical Society in 2002. He was a fellow of the MacArthur Foundation in 1987 and in 1997 he was elected to the National Academy of Sciences.

Prof. Schwarz coauthored a new string theory textbook entitled `String Theory and M-Theory: A Modern Introduction,' which was published earlier this year by Cambridge University Press.

We can't resist ending this note quoting again from John Preskill's poem:

Because he never would give in,
Pursued his dream with discipline,
John Schwarz has been a hero to me.
So please, don't spell it with a "t"!

Ladies and Gentlemen, it's our honor and privilege to share with you the excitement of superstring theory by presenting this list of 5 breakthroughs that John Schwarz would like to see.
-- 2Physics.com Team]

5 most important breakthroughs that I would like to see in
SUPERSTRING THEORY
by John H. Schwarz

(1) Discovery of supersymmetry at the Large Hadron Collider (LHC):

Supersymmetry is an intrinsic feature of superstring theory, and therefore I am convinced that it exists at a fundamental level. The big question is whether it is broken at a sufficiently low energy (the TeV scale) that supersymmetry partner particles can be discovered at the LHC. There are several well-known arguments for why this is likely. Discovery of supersymmetry would not prove that superstring theory is the correct fundamental theory and nondiscovery would not prove that it is wrong. Still, if it is discovered, string theory would deserve credit for spawning the study of supersymmetry in the first place.

The experimental discovery of superpartner particles (and hence supersymmetry)would be very exciting for several reasons: It would set the agenda for experimental particle physics for decades to come ensuring the vitality of high-energy physics research. It would be enormously informative, leading eventually to the formulation of a "supersymmetric standard model'' extending the current standard model to much higher energies. Such a supersymmetric standard model would provide a much better target for string theorists to try to relate to Planck scale physics, where string theory is most directly applicable, by "top-down reasoning". String theorists would like to predict all of this in advance, of course,but that does not seem to be possible.

(2) Other experimental evidence for string theory:

Aside from supersymmetry, there are a number of other possible experimental signals for string theory that have been considered, and there may be others that nobody has thought of yet. In my opinion, all of the following are unlikely to be observed, because the Planck scale (the natural energy scale of quantum gravity) is so far beyond what is experimentally accessible. However, there are scenarios in which quantum gravity phenomena can extend to much lower energies, and thereby possibly become observable, which certainly are worth exploring. The methodologies for making such a discovery fall into two broad categories: astronomical/cosmological observations and accelerator experiments. The first category can look for cosmic strings, primordial gravity waves, and certain subtle features of the cosmic microwave background. Accelerators, such as the LHC, can look for signals indicating the presence of extra dimensions, black holes, gravitons, or fundamental strings.

(3) More fundamental formulation of string theory/M-theory; emergent spacetime :

The current understanding of string theory is based on perturbation theory expansions of various symmetrical limits supplemented by a beautiful web of conjectured duality relations. What is missing is a single complete formulation of the theory that accounts for these various symmetrical limits and dualities. Such a formulation is likely to implement some deep principle that has not yet been recognized. It is also likely to be completely unique without any adjustable parameters or other features that can be altered.

There are various reasons to believe that the existence of space and time is not something built into the theory itself, but rather emerges as a property of certain classes of solutions. If this is correct, the theory will be radically different from any previous physical theory all of which describe what happens in a given spacetime. Even Einstein's theory of gravity (the general theory of relativity), in which the geometry of spacetime is determined dynamically,assumes the prior existence of a spacetime manifold.

(4) Determine whether time is emergent and clarify the status of quantum mechanics:

The previous item suggested that space and time are emergent properties of solutions to string theory rather than intrinsic features of the underlying theory. There is considerable evidence for the emergence of spatial dimensions in various settings, but there is no compelling evidence for the emergence of time. Experience with relativity makes it hard to imagine that space and time could be radically different in this regard. On the other hand, the notion of time is central in quantum mechanics, which is formulated as unitary time evolution. If time is emergent, some extension of the rules of quantum mechanics would seem to be required. The consistency of string theory requires that quantum mechanics is exactly correct. I am not questioning that this will continue to be the case in the future, only that quantum mechanics may need to be generalized somewhat to extend its domain of applicability.

(5) Determine the correct solution of the theory:

A unique equation can have many different solutions. By the same token, string theory can describe a rich variety of physical realities. We are still in the early stages of mapping out the possibilities, but the indications are that the number of possibilities is enormous. The picture that has been proposed, whose validity is not completely evident, is that there is an energy function that is a complicated function of many variables (called moduli) and that each of the minima of this function corresponds to a different solution of the theory. Assuming its validity, this picture raises a lot of questions: How is the "correct'' solution (i.e., the one that describes the Universe that we observe) determined? Is it a cosmological accident or is there some other principle? How can we determine the correct solution? How much empirical information needs to be input in order to determine it uniquely and make everything else computable (in principle)? These types of questions are very important to explore. They are stimulating a lot of serious research, as well as some spirited debate that is even spilling over into the public domain.

Merging Spintronics and Plasmonics: Evidence of Spinplasmonics

Photo: Prof. Abdulhakem Elezzabi, Professor & Canada Research Chair, Department of Electrical and Computer Engineering, University of Alberta, Canada

Researchers at the University of Alberta (Edmonton, Canada) and the Naval Research Laboratory (Washington, D.C., U.S.A.) have demonstrated a novel approach for the active control of terahertz plasmonic propagation. Using an ensemble of sub-wavelength size ferromagnetic/nonmagnetic spintronic structures, their experiments provide the first evidence of low frequency plasmonic conduction controlled via the electron-spin. Such phenomenon can be conceptualized as the photonic analog to the electrically-driven spin accumulation that serves as a basis for spintronic devices. The team is led by Prof. Elezzabi of University of Alberta.

In their experiments, the researchers employ a rudimentary plasmonic system consisting of ferromagnetic particles coated with nonmagnetic nano-layers. The excitation of the particles with a single-cycle, 1 picosecond wide electric field pulse induces nonresonant particle plasmons on the surface of the bimetallic particles. The dipolar electric fields associated with the particle plasmons on individual particles couple from particle to particle via nearest neighbor interaction and radiate into the far-field at the edge of the sample as coherent terahertz radiation.

When a magnetic field is applied to the sample, electron spin induced resistivity changes within the skin depth of the particles are mapped onto a modulation of the radiated electromagnetic fields. The researchers demonstrate that terahertz radiation propagated through the spintronic particles exhibits increased magnetic field dependent amplitude attenuation and phase modulation, nearly an order of magnitude larger than that of bare ferromagnetic particles.

The electron spin induced attenuation increases as the surface coverage of the nonmagnetic layer increases, showing that the striking enhancement of the magnetically dependent attenuation is attributed to the nonmagnetic layer.

The physical mechanism underlying the enhanced attenuation arises from non-equilibrium accumulation of electron spin electromagnetically driven from the ferromagnet into the nonmagnet (spin polarized surface currents). A quantitative measurement of the dependence of the attenuation on the nonmagnet layer thickness is in very good agreement with the spin diffusion length predicted by the spin accumulation model, as well as with other experimental measurements of this length scale.

Conceptual illustration of a nonresonant particle plasmon excited on a spintronic structure consisting of a sub-wavelength size ferromagnetic (Co) particle that has been coated with nonmagnetic (Au) layers. Shown below are the density of spin-up and spin-down electron states, N(E), in the ferromagnetic and nonmagnetic media. In an applied magnetic field, spin polarized electrons in the ferromagnet are electromagnetically driven into the nonmagnet layer, which results in excess interface resistance. The electron-spin induced resistivity change is mapped onto a modulation of the fields re-radiated from the non-resonant particle plasmon.

The demonstration of a spin-dependent photonic phenomenon opens up a novel avenue in both the fields of spintronics and photonics. The ability to magnetically manipulate near-field mediated light transport on metallic particles via electron spin promises another degree of freedom in the design of photonic devices. The researchers envision the development of solid-state, magnetically sensitive terahertz photonic switches, modulators, and band-pass filters based on electron spin.

Reference:
"Electron-Spin-Dependent Terahertz Light Transport in Spintronic-Plasmonic Media,”
by K. J. Chau, Mark Johnson, and A. Y. Elezzabi,
Physical Review Letters 98, 133901 (Link to Abstract)

High Energy Physics : 5 Needed Breakthroughs -- Guenakh Mitselmakher

[ Our guest today in the ongoing feature,
'5-Breakthroughs' is Guenakh Mitselmakher, Distinguished Professor of Physics and Director of the Institute for High Energy Physics and Astrophysics at University of Florida, Gainesville.

Currently, he is also the leader of the Muon system development for the CMS detector. CMS is one of two major universal detectors at the Large Hadron Collider at CERN, Geneva, Switzerland, which will begin operations in 2007-2008. He is also a member of the LIGO Science Collaboration, looking for the so called "burst" signals of Gravitational Wave (signals of limited duration), which may originate at a variety of astrophysical sources like supernova explosion.

In the long career starting from his PhD work in 1974 at the Joint Institute for Nuclear Research, Dubna, Russia, Prof. Mitselmakher made numerous important contributions in the field of Experimental high energy physics. Notable among those are studies of the lepton number conservation in rare decays of muons, investigations of the electromagnetic structure of pions, including the first measurements of the pion charge radius and polarizability, studies of the Standard Model and Beyond with the DELPHI detector at CERN and with the CDF detector at Fermilab. He also proposed a new type of Particle detectors (what is now called Quantum Calorimetry or bolometry), now broadly used in Paricle Physics and Astrophysics.

Here are 5 important breakthroughs that Prof. Mitselmakher would like to see in High Energy Physics.
-- 2Physics.com Team]

1. To understand the origin of "Dark Energy".

2. To understand the origin of "Dark Matter".

3. To find the Higgs or an alternative explanation for the spontaneous symmetry breaking in the Standard Model.

4. To explain (and calculate) the parameters of the Standard Model, such as masses and mixing angles of quarks and leptons.

5. To test if quarks (and other particles considered to be point-like) have a substructure.

Interferometric Detection of Gravitational Waves : 5 Needed Breakthroughs -- Rana Adhikari

[Rana Adhikari is a young, charismatic and dependable leader in the field of gravitational wave interferometry. His knowledge and experience with the operation of LIGO detectors with its variety of noise sources, feedback loops and subsystems are held in high respect by his fellow researchers. (Note: LIGO Laboratory operates 3 L-shaped long-baseline interferometers at two locations: Livingston, Louisiana has one of 4 Km arm length and Hanford, WA has one of 4Km and another of 2 Km armlength within the same vacuum enclosure) .

Rana started working on laser interferometers in LIGO around the turn of the century as a graduate student at MIT. He spent some time living with the Livingston interferometer and helped to reduce the noise in all 3 of the LIGO interferometers. In 2005, he received the first LIGO thesis prize. On that occasion, his thesis-supervisor Rai Weiss said,"He taught us how to make the interferometers sing and did this with wit and good humor coupled to precision and clear thinking".

Now, as an Assistant Professor of Physics at Caltech, he works on designing, prototyping and debugging the next generations of interferometric observatories. Here is a list of 5 breakthroughs Rana would like to see in gravitational wave interferometry.
-- 2Physics.com Team]

1) Development of the 'wonder' material (e.g. ultra hard Fullerite): capable of being grown to a 1 ton mass and a 1 meter diameter. Would be incredibly high purity (no mechanical loss), high thermal conductivity (no thermal lens) and very low thermal expansion. In one stroke this would make interferometric detectors immune to quantum radiation pressure noise, lower thermal noise (especially because of larger beam size), and reduce noise due to stray forces.

2) Neural networks for tuning the all digital control systems: in the future the machines will run simulations exploring the possible parameter space of mirror positions, laser power, feedback topologies, etc. They will also then tune themselves for maximum sensitivity and iteratively design their own signal analysis algorithms with only qualitative input from scientists.

3) More Laser Power: the upcoming generation of interferometers in 2011 will be able to sense a part in 10¹¹ of a wavelength. This sensitivity will scale with the square root of the laser power. Quiet lasers with ~10 kW power levels would enable interferometry good enough to hear coalescing binaries anywhere in the universe.

4) Long baseline interferometers: 50 km scale interferometers would reduce the contribution of the low frequency (displacement) noise by a factor of 10 in a very clean way. One can find such sites using Google Earth.

5) Squeezed light injection through the interferometer's dark port to reduce the 'shot noise', phase sensing limit. With 1 ton masses (reducing the effects of photon pressure fluctuations) and very long arms, the gravitational wave sensitivity would be 30 to 300x better than the current generation and only limited by light scattering off of the 10^-8 torr of residual molecular hydrogen in the interferometer's beam tubes. Doing better than the LIGO vacuum system would be a real challenge.

Upcoming Physics Conferences

Here is a selected list of forthcoming conferences in Physics. You are welcome to freely advertise Physics jobs or conferences in 2Physics by sending an email to 2Physics@gmail.com.

April 10-13: BICOS 2007 -- Bilbao Encounter On New Standard Cosmology (Bilbao, Spain)
April 23-27: Advanced computing and analysis techniques in physics (Amsterdam, The Netherlands)
May 10-12: The Hunt for Dark Matter: A Symposium on Collider, Direct and Indirect Searches (Fermilab, Batavia, IL)
May 12-16: Black Holes VI (White Point Resort, Prince Edward Island, Canada)
May 14-17: Origins of dark energy: conference and workshop (Hamilton, Canada)
May 14-18: Dark side of the universe (Villa Olmo, Italy)
May 14-18: Intl workshop on quantum noise (Caloundra, Australia)
May 18-20: 12th Canadian Conference on General Relativity and Relativistic Astrophysics (Fredericton, New Brunswick, Canada)
May 18-20: Workshop: excursions in the dark (Waterloo, Canada)
May 20-26: Matter and Energy in the Universe: from nucleosynthesis to cosmology (Chateau de Blois, France)
May 28-June 22: Theoretical advanced study institute (TASI) in elementary particle physics: "String Universe" (Boulder, Colorado, USA)
June 1-5: Central European workshop on quantum optics, 14th edition (Palermo, Italy)
June 4-7: 6th intl conference on nuclear and radiation physics (Almaty, Kazakhstan)
June 5-9: Annual APS Division of Atomic, Molecular and Optical Physics Meeting (Calgary, Canada)
June 10-13: From Quantum to Cosmos II -- Space-based Research in Fundamental Physics and Quantum Technologies (Bremen, Germany)
June 10-13: Intl conference on quantum information (Rochester, NY)
June 11-22: Summer school on particle physics (Trieste, Italy)
June 11-29: Physics at TeV colliders (Les Houches, France)
June 16-20: 4th intl workshop on quantum chromodynamics - theory and experiment (Bari, Italy)
June 18-20 SciNeGHE07: Fifth Workshop on Science with the New Generation of High Energy Gamma-ray Experiments (Villa Mondragone, Frascati, Rome, Italy)
June 18-22: School on attractor mechanism (Frascati, Italy)
June 22-July 3: 19th Petrov school -- summer school-seminar on recent problems in theoretical and mathematical physics (Kazan, Russia)
June 26-29: Physics in collision symposium on elementary and astro-particle physics (Annecy, France)
July 2-7: 13th intl symposium on particles, strings and cosmology (London, UK)
July 2-27: ESF school of theoretical physics: string theory and the real world (Les Houches, France)
July 7-10: Vienna symposium on the foundations of modern physics (Vienna, Austria)
July 8-14: 7th Edoardo Amaldi Conference on Gravitational waves (Sydney, Australia)
July 13-14: String and M theory approaches to particle physics and cosmology (Florence, Italy)
July 13-17: 'Cosmology and Strings' Workshop (ICTP, Trieste, Italy)
July 26-August 1: 15th intl conference on supersymmetry and the unification of fundamental interactions (Karlsruhe, Germany)
July 30-August 4: 25th intl symposium on lattice field theory (Regensburg, Germany)
July 30-August 11: Cosmology and particle physics beyond the standard models (Cargese, France)
August 16-18: 11th Paris cosmology colloquium (Paris, France)
August 16-18: Windsor summer school on condensed matter theory: quantum transport and dynamics in nanostructures (Windsor, UK)
August 20-24: Exploring QCD: deconfinement, extreme environments and holography (Cambridge, UK)
August 23-29: 13th Lomonosov conferences on elementary particle physics (Moscow, Russia)
September 2-6: Photons, atoms, and qubits (Royal Society, London, UK)
September 3-7: 3rd intl conference on physics and control (Potsdam, Germany)
September 2-7: Quantum Field Theory (Leipzig, Germany)
September 10-14: Intl workshop on topological quantum computing (Dublin, Ireland)
September 11-15: 19th intl conference on topics in astroparticle and underground physics (Sendai, Japan)
September 11-14: Recent advances in quantum integrable systems (Annecy-le-Vieux, France)
September 15-22: New trends in high-energy physics (Yalta, Ukraine)
September 24-28: 6th intl Heidelberg conference on dark matter in astro & particle physics(Sydney, Australia)
September 24-28: 4th intl conference on flavor physics (Beijing, China)
October 1-5: Planets to Dark Energy (Manchester,UK)
October 11-13: Algebra, geometry, and mathematical physics (Göteborg, Sweden)
October 28-November 2: 7th intl conference on complex systems (Boston, MA)
November 4-10: Noise, information and complexity at quantum scale (Erice, Sicily, Italy)
December 4-9: Intl conference on magnetic materials (Kolkata, India)